What type of message should always be written down?
a. a personal one
b. one that includes names, times, and telephone numbers
c. a negative message
d. if your memory is sharp enough, you won't have to write any messages down.

b. One that includes names, times, and telephone numbers

Receiving a message either for persona, business or other related transaction is important because of its content. Information is a key ingredient of every message. Moreover, here, messages that should always be noted are with names, time and mobile numbers because they provide data that might be helpful in conjunct to other scenarios.